(1) Field of the Invention
The present invention relates to a night-vision imaging apparatus, a headlight module, and a control method of the night-vision imaging apparatus. In particular, the present invention relates to a night-vision imaging apparatus which emits infrared light.
(2) Description of the Related Art
It is dangerous for a driver to drive a vehicle at nighttime due to poor visibility. An incidence of accidents during nighttime hours is much higher than an incidence of accidents during daytime hours at which the driver is good in visibility.
At nighttime, for example, a visible distance obtained by a low beam is short in bidirectional traffic, and most drivers fail in visible judgment. Consequently, the drivers are late with recognition of unilluminated obstacles, pedestrians, unlit bicycles and animals, leading to accidents. Under bad weather conditions such as rain, fog and snow, further, the visibility of the driver becomes worse.
In night driving, conventionally, a headlight for a vehicle switches between a low beam and a high beam in consideration of dazzling of a driver on an oncoming vehicle. Herein, the low beam is used for illuminating a road surface while the high beam is used for extending a visible distance. However, the switching operation between the low beam and the high beam is burdensome. In addition, use of the high beam disadvantageously causes dazzling of a pedestrian or a driver on an oncoming vehicle.
In order to solve such a problem, there has been proposed a night-vision imaging apparatus for a vehicle. According to this apparatus, far-infrared light generated from human beings and animals is captured by a far-infrared camera, and an image taken from the captured light is displayed. However, such a far-infrared camera capable of capturing far-infrared light is considerably expensive.
There has been also proposed a night-vision imaging apparatus for a vehicle. According to this apparatus, a bundle of near-infrared light at a wavelength of about 1 μm is emitted to a forward area of a vehicle, a bundle of the light reflected from an object on the forward area of the vehicle is received by a camera, and an image is taken from the received light.
For example, Japanese Unexamined Patent Application Publication No. 2003-045210 discloses a night-vision imaging apparatus for a vehicle. According to this apparatus, a camera receives a bundle of light reflected from an object on a forward area of a vehicle to take an image from the received light.
In Japanese Unexamined Patent Application Publication No. 2003-045210, a headlight disclosed in DE4007646A1 is described as the prior art. As disclosed in DE4007646A1, the headlight including a night-vision imaging apparatus has two headlights each using, as a light source, a laser diode which emits near-infrared light, in addition to a configuration of a normal headlight. In the headlight disclosed in DE4007646A1, an imaging CCD camera is placed on a roof region of a vehicle. In addition, a visible-light source such as a halogen lamp has a wide spectrum of several hundreds of nanometers in width.
In the case of using the aforementioned headlight including the night-vision imaging apparatus, it is necessary to reduce an influence of light emitted by an oncoming vehicle. In the headlight disclosed in DE4007646A1, for example, an optical bandpass filter is disposed forward an objective lens of the camera. The optical bandpass filter having a narrow transmission band can considerably attenuate visible light emitted by an oncoming vehicle. A spectrum of a laser beam is several nanometers in width; therefore, the optical bandpass filter having the narrow transmission band transmits such a laser beam. In the conventional headlight, further, the laser diode is driven by a pulse and a video camera to be used has an electronic lock operated in synchronization with a laser beam emitted by the laser diode; thus, the light emitted by the oncoming vehicle can be attenuated.